Heat exchanger

ABSTRACT

A heat exchanger from which is absent a dividing wall between an axial flow of hot fluid, preferably a flame, and an encircling spiral flow of fluid to be heated which is maintained separate by the centrifugal force due to its cyclonic flow and is contained by a refractory-lined wall which absorbs radiant heat from the hot fluid.

United States Patent [1 1 Waeselynck Nov. 20, 1973 HEAT EXCHANGER Raymond Waeselynck, Paris, France [73] Assignee: Stein Industries, Paris, France [22] Filed: Feb. 22, 1971 [21] Appl. No.2 117,803

Related US. Application Data [62] Division of Ser. No. 813,438, April 4, 1969, Pat. No.

Inventor:

[52] US. Cl. 263/19 A, 60/39.69, 165/1 [51] Int. Cl. F231 9/04 [58] Field of Search 60/DIG. 8, 39.15, 60/39.18 C, 39.18 B, 39.66, 39.69; 165/1;

[56] References Cited UNITED STATES PATENTS 9/ 1949 Goddard 60/DIG. 8 5/ 1961 2,985,438 Prowler 263/19 A 2,619,798 12/1952 Strub 60/39.18 C

3,621,654 11/1971 Hull 60/39.15 2,933,296 4/1960 Spangler 263/19 A FOREIGN PATENTS OR APPLICATIONS 869,355 5/1961 Great Britain 165/] Primary Examiner-Carlton R. Croyle Assistant Examiner-Warren Olsen Att0rneyEric I-I. Waters et a1.

[5 7 ABSTRACT A heat exchanger from which is absent a dividing wall between an axial flow of hot fluid, preferably a flame, and an encircling spiral flow of fluid to be heated which is maintained separate by the centrifugal force due to its cyclonic flow and is contained by a refractory-lined wall which absorbs radiant heat from the hot fluid.

3 Claims, 4 Drawing Figures HEAT EXCHANGER This Application is adivision of application Ser. No. 813,438 filed Apr. 4, l969, and issued as US. Pat. No. 3,642,061 on Feb. 15, 1972. o

The present invention relates to apparatus in which two fluids flow and exchange heat.

In heat exchangers of known type, the two fluids flow on either side of a fluid-tight wall, which is at the same time the seat of the heat exchange, this wall being formed as tubes, flues, etc. The wall has to resist thermal and mechanical stresses as well as chemical attacks resulting from the elevated temperatures to which it is subjected. Its price is therefore high, its reliability is problematical and the exchange temperatures are limited tovalues compatible with its resistance. Finally, if one or the other of the wall faces is exposed to a corrosive fluid'or afluid charged with impurities, the deposits formed are dangerous for the safety of the heat exchanger and reduces its efficiency.

The present invention relates to a heat exchanger which does not have the above-mentioned disadvantages because of the absence of separation walls between the two heat-exchanging fluids.

An apparatus according to the invention comprises an'enclosure formed as a body of revolution, equipped with an axial inlet and outlet for the passage of the hot fluid, a tangential inlet and outlet for the fluid to be heated and means for ensuringrotation of the fluid to be heated at a velocity sufficient for the centrifugal force to maintain it in the vicinity of 'the wall of the enclosure between the tangential inlet and outlet.

The internal wall of the enclosure is preferably lined with arefractory-materi'al resistant to attack at the high temperature of the fluid to be heated with which it is in contact, having an absorbent power as close as possible to thatof black body absorption, and having a surface as extended as possible, arranged for promoting convection but for -'limiting'turbulence in contact with the fluid tobe heated. For example, the refractory material lining, which may be steel, ceramic, etc. may comprise sections of helical fins.

The hot fluid passing axially through the enclosure may result from combustion controlled to produce a flame of large surface which radiates strongly. o

In one embodiment of the exchanger according to the invention one or "more longitudinal slits are provided in the wall of the enclosure for recovering the solid particles which maybe taken up by the fluid'to be heated, the apparatus then acting simultaneously as a separating cyclone.

In an exchanger according to the invention, the axial hot fluid heats by radiation the internal surface of the enclosure, which supplies this heat by convection to the fluid to be heated having a helical movement. The hot fluid may result, for example, from the-combustion of an oil fuel, while the 'fluid to beheatedmay be air, for example. The differencesin the angular velocities, densities and viscositiesare practically'opposed, as shown by'experience, to mixingof the combustion gases and air to be heated, such that the latter is practically uncontaminated ifits removal at the'outlet'is suitably limited by a closure device. Th'e'comb'ustion gases which leave at a temperature which is still high, may be sent to a boiler or a conventional heat exchanger, in which thefue'l and combustion air are preheated before their introduction into the burner with which the apparatus according to the invention is equipped.

This type of heater according to the invention, in which exchanges at the highest temperatures occur without an intermediate wall, does not have most of the disadvantages of conventional exchangers. Thus, the convection surfaces, which may be cut out as desired, are practically not subjected to either thermal or mechanical stresses; theirexpansion takes place freely and fluid-tightness is not necessary; they are protected from contact with the combustion gases and are consequently insensitive to their attack; they have simply to resist the chemical attack of the fluid to be heated which, in most cases, is a clean and homogeneous, possibly neutral, gas. Finally if deposits are produced, their effect is not to destroy but to protect the walls against radiation; at the most they may modify their coefficient of absorption.

The efficiency of the exchanger according to the invention, defined as the ratio of the quantity of heat exchanged by radiation to the calorific value of the fuel, is higher, the higher is the temperature of the flame itself, that is to say, the higher the temperature to which the combustion air has been previously heated. When the fluid to be heated is not air, the burner receives its combustion air separately. In the cases where the fluid to be heated is air, if the heat exchanged by radiation represents for example 50 percent of the calorific value of the fuel, and if the combustion air is admitted at a temperature of 400C, it is sufficient to take a small fraction (about one-fourth) of the total air to ensure combustion, the principal part of the air being heated to 800 or 900C by contact with the wall.

This type of heater will find applications whenever a slight entrainment of combustion gas in the heated fluid is not a serious disadvantage. It may be applied for example to the feeding of two gas turbines operating simultaneously: in one of them the combustion gases are expanded after their passage through a conventional exchanger (boiler, tubular air heater), which reduces their temperature to a value acceptable for'the'gas turbine (for example 630C if the fuel is unrefined heavy fuel); the other gas turbine receives the gases which are uncontaminated and are heated to high temperature (for example 800 to 900C), and the weight of which is several times that of the combustion gases. Despite the use of unrefined heavy fuel, the second gas turbine, which is much larger, thus operates on a thermodynamic cycle of high efficiency without danger of corrosion.

The following additional description, with reference to the accompanying drawings, given mainly as an example, is intended to illustrate the invention.

In these drawings:

FIG. 1 is a diagrammatic axial section of a radiation gas heater according to the invention;

FIG. 2 shows diagrammatically an exchanger according-to the invention used for the feeding of gas turbines,

FIG. 3 is a diagram showing the application of the invention to heating the superheaters of a boiler, and

FIG. 4 is an axial section showing in greater detail the elements in'FIG. l.

A fluid heater according to the invention, such as is shown in FIG. '1, comprises an enclosure formed as a body of revolution 1, for example abody which is cylindrical, conical etc., provided withan axially arranged inlet 2 and an outlet 3. The inlet 2 may receive a hot combustion-supporting gas associated with a fuel inlet conduit 4, or a combustible mixture, intended to burn in the interior of the enclosure, the outlet 3 serving for the outflow of the hot gas formed of the combustion gases in the example shown. The enclosure also comprises an inlet 5 and a tangential outlet 5a for the fluid to be heated. For this purpose, a centrifugal generator in the form of vanes 7 or a volute, etc. may be provided. The cold fluid set in rotation, for example by the vanes 7, should to have a sufficient velocity for it to be kept by the centrifugal force in the vicinity of the wall 1 along the entire length of the latter. The inlet for the fluid to be heated is generally so arranged that this fluid and the heating fluid flow in parallel currents; the arrangement may, however, also be such that the flows are in counter-current. In FIG. 1, the flows are in tandem and the tangential inlet 5 is close to the inlet 2, while the tangential outlet 5a is close to the axial outlet 3. The intake of the heated fluid is regulated by varying the relative vacuum in the outlet conduit 6.

In addition, the wall of the enclosure 1 is preferably provided with helical convection vanes 8.

Finally, in the embodiment shown, there is provided some preheating of the air, which entering at 9 flows along the enclosure 1, owing to a jacket 10 concentric with this wall, before being admitted at 5 through the vanes 7.

Such an apparatus is of simple construction and does not necessitate the provision of material resistant to very high temperatures, the wall of the enclosure 1 being continuously cooled by the fluid to be heated. The risk of corrosion of the walls is thus obviated.

The exchanger may be used for heating any gaseous or liquid fluid. In the latter case, it may be used, for example, for the gasification of any liquid (including a fuel), the latter being preferably finely sprayed in the gas already produced and carried in closed circuit in contact with the wall of the exchanger.

If the fuel to be heated is air, the latter may be used for domestic purposes; indeed, the apparatus may be regulated such that the air is practically free from combustion gases.

FIG. 2 shows the application of an exchanger according to the invention to the feeding of a mixed installation generating power from two gas turbines. In this case, the furnace is at the pressure prevailing upstream of the turbines; the turbine 11, by far the more powerful, has passing through it the clean gas 14, heated to an elevated temperature, for example 850C; the turbine 12 receives only the combustion gases after the latter have been cooled in an exchanger 15 to a temperature compatible with the use of gases containing flue' dust and corrosive gases, for example 630C. As indicated in the foregoing, the exchanger 15 may serve either to heat the clean gas (for example air) and combustion air before their introduction at 16 into the furnace 13, or to produce or superheat steam, or to heat boiler feed-water. Finally, the clean gas may flow in a closed circuit and under high pressure, passing successively through the furnace 13, turbine 11 and coolerexchangers before being re-introduced into the inlet of the compressors. The combustion gases, on the contrary, are discharged to the outside after passing through the turbine 12 and outlet exchangers or economizers. However, these combustion gases may be neutralized, purified and filtered wholly or in part, so as to form the gas of the actual circuit, and compensate any losses of the latter.

Another application of the invention is that of heating boiler superheaters (or any other high-temperature exchangers) as shown in FIG. 3.

The heater furnace according to the invention and here shown at 18, produces a high-temperature neutral gas 19, which passes through the conventional tubular exchanger 20 (superheater, resuper-heater, complete boiler, or any heater), and flows in a closed circuit owing to a pick-up blower 21 which compensates for pressure losses. The furnace 18 acts as a cyclone and eliminates any solid particles in suspension. These particles are discharged from time to time from the furnace, the internal wall of which comprises at least one longitudinal slit acting as a dust trap, and some orifices, through which this dust is intermittently driven. The gas in circulation is clean, and the attacks by erosion or corrosion at elevated temperature are reduced.

By varying the speed of the blower 21, the level of the exchanges in 20 may be regulated; for example, the superheat temperature may be regulated if 20 is a superheater.

This application is particularly adaptable in the case of an installation with a mixed gas-steam cycle, with a boiler through which the gases pass under pressure, where the furnace 18 is under pressure and 20 is the high-temperature part of the boiler, while the evaporator tube nest is situated at the outlet of the combustion gases from the furnace 18. The use of a clean gas in 20 eliminates the serious risks of rapid fouling and permits the use of compact tube nests. In addition, the limitation to 800 or 850C of the temperature of the gas passing through 20 considerably reduces the risk of bursting or rupturing of the tubes by overheating in case of difficulty in the circulation or abrupt variation in load. The gas turbine is then fed by an outlet at 22 of clean and hot gas upstream of the exchanger 20, the replacement gas arriving at inlet 23 upstream of 21.

Another application is that of heating without oxidation before forging, rolling or wire-drawing, or the heat treatment in controlled atmosphere of various metallurgical products (tubes or parts of high-alloy steel, or of non-ferrous metals, for example). In this case, it is .merely necessary to suitably select the gas passing through the container 20 in which the parts to be heated are placed.

An exchanger constructed in accordance with the invention may also be used in drying installations. It is known that drying installations necessitate the production of a considerable flow of fluid at elevated temperature, and also a mechanical device for conveying the materials to be dried. These two conditions may be met by an exchanger according to the invention; for this purpose, the exchanger is selected to have a sufficient working pressure for the combustion gases to feed a turbine serving for the mechanical conveying of the materials to be dried; the hot fluid, consisting of air, is thus at a high pressure and is therefore expelled from the apparatus at a high velocity. The range of regulation of the apparatus will be so much greater if in this case it is possible to accept a certain proportion of combustion gases in the hot air.

Yet another application is that of domestic heating, the clean gas then being simply air which, heated directly in the furnace, leaves the latter almost free from any trace of combustion gases.

It is obvious that the embodiments described have been given mainly as examples and that they may be given numerous modifications without going beyond the scope of the present invention. The application examples are also not restrictive, the apparatus according to the invention being utilizable in all cases where a very simple heater is desired and where very slight pollution by combustion products is not unacceptable.

I claim:

1. A fuel burner comprising an outer hollow casing having opposite ends, an inner hollow casing disposed within the outer casing in annularly spaced relation, means for supplying air into the space between the casings, said inner casing having an inlet at one end thereof for flow of air from the annular space into said inner casing, fuel burner means disposed in said inner casing adjacent said inlet for producing a flame within said inner casing, said inner casing having a second inlet for flow of air from the annular space into the inner casing, centrifugal generator means at said second inlet for producing helical flow of the air in the inner casing passing through said second inlet, said inner casing including helical convection vanes facing said second inlet for flow of the air from the centrifugal generator means through the inner casing such that the air flowing in the helical convection vanes can be directly heated by the flame while remaining relatively unmixed with the combustion gases produced by the fuel burner means, first outlet means facing said fuel burner means and disposed at the other of the ends of the inner casing for discharge of the combustion gases therefrom, and second outlet means at the periphery of the inner casing and leading to said helical convection vanes for discharge of now heated air from the inner casing.

2. A fuel burner as claimed in claim 1 wherein said means for supplying air into said space comprises an inlet in said outer casing at the end thereof opposite the inlet into said inner casing whereby the air flows through said annular space so as to be preheated therein before it enters the inner casing.

3. A fuel burner as claimed in claim 1 wherein said outer casing is constituted as a body of revolution. 

1. A fuel burner comprising an outer hollow casing having opposite ends, an inner hollow casing disposed within the outer casing in annularly spaced relation, means for supplying air into the space between the casings, said inner casing having an inlet at one end thereof for flow of air from the annular space into said inner casing, fuel burner means disposed in said inner casing adjacent said inlet for producing a flame within said inner casing, said inner casing having a second inlet for flow of air from the annular space into the inner casing, centrifugal generator means at said second inlet for prOducing helical flow of the air in the inner casing passing through said second inlet, said inner casing including helical convection vanes facing said second inlet for flow of the air from the centrifugal generator means through the inner casing such that the air flowing in the helical convection vanes can be directly heated by the flame while remaining relatively unmixed with the combustion gases produced by the fuel burner means, first outlet means facing said fuel burner means and disposed at the other of the ends of the inner casing for discharge of the combustion gases therefrom, and second outlet means at the periphery of the inner casing and leading to said helical convection vanes for discharge of now heated air from the inner casing.
 2. A fuel burner as claimed in claim 1 wherein said means for supplying air into said space comprises an inlet in said outer casing at the end thereof opposite the inlet into said inner casing whereby the air flows through said annular space so as to be preheated therein before it enters the inner casing.
 3. A fuel burner as claimed in claim 1 wherein said outer casing is constituted as a body of revolution. 